Changes in sensitivity of Sclerotinia homoeocarpa to the demethylation inhibitor fungicide propiconazole
Samples of 'Sclerotinia homoeocarpa' were collected from the same locations sampled in a 1994 baseline fungicide sensitivity study, plus two other locations in southern Ontario. At least 50 isolates from each site were tested for propiconazole sensitivity by growing them on propiconazole-amended media and calculating EC50 values. The DMI-treated populations were significantly less sensitive than the baseline populations as well as the untreated populations. To test for cross sensitivity between DMI and other fungicides, 70 isolates were plated on discriminatory concentrations of 1 [mu]g/ml iprodione or 1 [mu]g/ml benomyl. No significant correlation was found between sensitivity toward propiconazole and benomyl. A weak correlation was found between DMI and iprodione sensitivity. All isolates were plated with vegetative compatibility group (VCG) tester isolates to see whether the less sensitive isolates were of the same origin. No correlation was found between VCG and propiconazole sensitivity.